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Observations and Instrumentation 1

by: Stephan Kuvalis

Observations and Instrumentation 1 ASTR 3510

Marketplace > University of Colorado at Boulder > Astronomy > ASTR 3510 > Observations and Instrumentation 1
Stephan Kuvalis

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Class Notes
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This 6 page Class Notes was uploaded by Stephan Kuvalis on Thursday October 29, 2015. The Class Notes belongs to ASTR 3510 at University of Colorado at Boulder taught by Staff in Fall. Since its upload, it has received 22 views. For similar materials see /class/231967/astr-3510-university-of-colorado-at-boulder in Astronomy at University of Colorado at Boulder.


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Date Created: 10/29/15
Advanced IRAF Commands Now that you7ve gotten the hang of the basics like imeamme and using d39 its time to move on to some new commands Phelp The task phelp is one of the most useful you7ll nd in lRAF It will bring up a help page on any lRAF task The syntax for using phelp is as follows clgtphelp imexamine This will bring up the help page for imexamine At the top of the page you can nd where within the lRAF packages imexamine exists In this case it is tvimexamine First it lists the possible input parameters Required parameters are always listed rst and then other possibilities come next After that you get a brief description details on the interactive options and a couple of examples on usage To move around in the help page you can press the spacebar return d or N key to move down different amounts and the u or P key to move up Looking Through the IRAF Packages lRAF has a set of premade routines that are set up in a kind of directory system just like the directories and les in your cosmos account In order to open some packages you have to be in the correct directory You can nd the directory path you want using phelp described above From now on FM call directories within lRAF packages and the commands tools In order to list the packages amp tools available to you where you are use the 9 key To list all packages and tools use 9 Now if I want to move into a speci c package from where lRAF starts for example images I type clgtimages and get the response imcoords im t immatch tv im lter imgeom imutil This is now a list of packages available to move into lf 1 want to leave the images package I type bye Command History So by now you7ve probably realized that lRAF wont let you use the up arrow to retrieve commands you7ve previously used lnstead to access this command history rst type 6 and return You should see something like this clgte images if going into the images package is the last thing you7ve done You can now access the command history by using the up and down arrow keys Epar The command epar stands for edit parameters ie it opens a screen and displays all of the possible parameters that you can supply For example if I type clgtepar implot I see the following screen PACKAGE plot TASK implot image image to be plotted line line to be plotted wcs logical world coordinate system step 0 Step in pixels for jk key coords graphics cursor input device stdgraph graphics device for plots mode ql I can now move through these options using the arrow keys and enter the appropriate values For example if I wanted to implot the image m56 ts the line would look like image m56 ts image to be plotted Note that parameters that require input are the rst listed with optional parameters listed afterwards with parenthesis around them Once you have lled in the values to your pa rameters you can quit and save by typing 39q or you can run the task with 90 If you ever want to look at the paramters already lled in for a task lRAF will remember what you last did you can use the list parameters command lpar eg clgtlpar implot M irzftevm Implot After imexamme the command implot image plot is one of the most useful Implot takes a 3 dimensional image chooses a single line or column from that image and plots it 2 dimensionally This is very useful for looking at the intensities in each pixel along a single line or column For example imagine you have an image of a star called star ts To implot I type clgtimplot starfits A window like the two displayed above will pop up with red crosshairs that you can move around There are many different options that you can utilize in this interactive mode To list this make sure the pop up window is active and type 9 After you7re done in this screen type 1 twice to quit A quick command to nd the value at any given pixel position is ot move the vertical crosshair to the desired location and type spacebar Two of the most useful are the commands that tell which line y position from ds9 or column x position from ds9 you would like to plot To plot column n I type c n within the interactive window A yellow line showing your command will popup at the bottom of the window when you begin typing The same thing works for choosing a line 1 n Now that you can specify which line to plot you may want to blow up a portion of the plot for closer examination This is done through the e expand command Use the crosshairs to mark out the lower left and upper right corners of the box that will become your new plot range First put the crosshairs where you would like the lower left corner to be type 6 move the crosshairs to the upper right and type 6 again Note that it prompts you at the bottom of the screen If you don7t like the result type T for redraw the original line and try again After zooming in on the profile of a star you might want to measure it just like in imexam The way to do is using the p command Place the horizontal cross hair in the middle of the background noise and the vertical cross hair on the left side of the stellar profile and type p You want this be significantly far from the wings of the star so as to get a good measure of the background Now move the cross hairs to the righthand side of the star keeping the horizontal one in the background noise and type 17 again At the bottom of the screen the measurements describing the pro le will pop up There are four bars of information that you can move through using the key The rst bar gives the line or pixel describing the 2 D centroid the full width at half max denoted by a dashed line overplotted on the screen the peak value and the background level The other bars give moments of the background subtracted data A last interactive command is the 8 command It works essentially the same way as the pro le command by bounding a region with the crosshairs and typing 8 twice The output is then basic statistics of the region the median mean standard deviation rms sum and number of pixels in the designated region To leave the implot interactive environment simply type 1 and you7re lRAF command line will become active again Imcopy At some point you may want to copy an image within lRAF to a new le for example as a backup While the UNIX command 0p will accomplish transferring the entire image to a new le you may want to only transfer a portion of the new image This is done through the imcopy command The basic idea is that you can specify the region in pixels to transfer So if I want to copy from pixel 400 to 500 in the x direction and pixel 600 to 700 in the y direction I would type clgtimcopy f56 ts400500600700 f56new ts Now I have a new ts le that is only 100 X 100 pixels as opposed to 1024 X 1024 pixels Imarith Once we begin using calibration frames in data analysis you7ll need to perform basic arith matic functions on images The command imarith is the quickest way to accomplish this within lRAF In order to use imarith I suggest clgtepar imarith You need to ll in the name of image or a number the operand min max a second image or number and what the result will go into lfl wanted to subtract the image dark ts from the image science ts and put the result in nal ts my screen would look like PACKAGE imutil TASK imarith operandl science ts Operand image or numerical constant op Operator operand2 dark ts Operand image or numerical constant result nal ts Resultant image After lling in these values I would type 90 to activate the command sequence 1 can also do the same thing from the lRAF command line clgtimarith science ts dark ts nal ts Now there should be another image called nal ts in the same directory as the other im ages You can access this new image through ds9 imexam implot and any other lRAF command When you start doing more advanced image combinations there is another task imcombme that you7ll need to use but more info on that will come later Imstatistics Sometimes you7ll want to compute statistics over a region of several columns or rows of an image The correct task for this is imstat To calculate statistics on the region 400500600700 of image nal ts using imstat clgtimstat nal ts400500600700 The output looks something like this IMAGE NPlX MEAN STDDEV MIN MAX test ts400500600700 10201 1354 1559 48 794 You7ll nd this task extremely useful later on in the course when you need to do noise calculations Imheader Sometimes you might nd yourself needing some piece of information about your image that you forgot to record or something else While you should always record your obser vations carefully there is sometimes a way to recover this information Every ts le has two parts the actual image data and a header In this header is a list of information and keywords describing your observations To access the short version of this header for the image f56 ts clgtimhead f56 ts A line stating f56 ts10241024ushort pops up You get the image name and size but nothing else There is also a long version of this header accessed by clgtimhead f56 ts 1 The resulting output looks like f56 ts102471024ushort No bad pixels7 min07 maX0 old Line storage mode7 physdim 1024710247 length of user area 1053 su Created Wed 210745 13 Oct 20047 Last modi ed Wed 210745 13 Oct 2004 Pixel le 77f56 ts77 ok BSCALE 1000000000000e000 BZERO 3276800000000e004 BIAS 100 ORIGIN 7SBO 7 TELESCOP 7192 24 7 FOCALLEN 1920000000000e002 APERTURE 2400000000000e001 OBSERVER 7Observer 7 DATE OBS 72004 09 18 7 TIME OBS 7034053 7 CCDSFPT 1 CCDSUBFL 0 CCDSUBFT 0 CCDXBIN 1 CCDYBIN 1 EXPSTATE 293 TEMPERAT 4817803680962e000 INSTRUME 7SBIG ST 1001E1001XE7 E GAIN 2720000000000e000 XPIXSZ 2400000000000e 002 YPIXSZ 2400000000000e 002 SBIGIMG 9 FILTER 73 7 EXPOSURE 2000000000000e001 CBLACK 105 CWHITE 175 Most of this information will become invaluable as you do more advanced observations For now7 the keywords of importance to you are Filter the lter number Emposure erposure time in seconds Date and Time This is obviously a lot to absorb in one sitting Instead I suggest you use this as a reference document7 and try out these commands as you go Have fun7 good luck7 and don7t forget to ask questions if you get stuck


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